Selection of a network element

ABSTRACT

A method for delivering information on a serving mobile switching centre server for an user equipment between a first communication network and a second communication network. The method includes a step of requesting an attachment of the user equipment to the second communication network by signaling between the user equipment and a network node of the second communication network, the signaling including at least part of information on the mobile switching centre server serving the user equipment in the first communication network. Additionally, an user equipment and a network node implementing the aspects of the method are described.

TECHNICAL FIELD

The invention concerns in general the technical field of wirelesscommunication systems. More specifically, the invention concernsdelivery of information relating to a serving network node betweenwireless communications networks implementing different accesstechnologies.

BACKGROUND OF THE INVENTION

The evolution of wireless communications has resulted in an increase ofnetworks of different technologies and corresponding different airinterfaces. As a result, during the course of a single call, a wirelessuser equipment (UE) may roam among multiple radio access networks(RANs), wherein each such RAN implements a different technology to theother RANs of the multiple RANs, for example, a second generation (2G)and a third generation (3G) circuit switched RAN, such as a GSM (GlobalSystem for Mobile communications) network and WCDMA (Wideband CodeDivision Multiple Access) providing primarily circuit voice service, anda packet data RAN, such as a later generation 3GPP LTE (Third GenerationPartnership Project Long Term Evolution) network. As the UE roams amongthe circuit switched RAN and the packet data RAN providing packet dataservices, it may be beneficial to system performance to handover the UEbetween the circuit switched RAN and the packet data RAN for example dueto fact that channel conditions associated with the latter RAN may bemore favorable than the channel conditions associated with the formerRAN. By way of another example, an operator of both a legacy circuitnetwork and a packet data network may desire to move the UE from onesuch network to the other network for purposes of system load balancing.

In order to offer a successful roaming experience to the user theUE/user needs to register with the new network to receive services thatrequire registration. This registration process is described as NetworkAttachment. The attach procedure comprise inter alia some signalingrelating to identification of the UE and network elements relating toservice, security related issues, location update related signaling,bearer(s) allocation for the UE and IP address allocation, for example.FIG. 1 illustrates an E-UTRAN initial attach procedure according to 3GPPspecification TS 23.401 V10.5.0 (2011-09) in LTE (E-UTRAN). Theprocedure illustrated in FIG. 1 is only for background purposes forincreasing the understanding, what kind of process is performed, when UEattaches to LTE network.

As already indicated, LTE technology is primarily supporting packetbased services only. However, current services in the GSM/WCDMA networksare mainly based on circuit switched (CS) technology. An example of sucha service is voice communication. It is noticed that as long as theservices based on either packet based or CS technology co-exist, thereis need to support the functionality of the service in all networks. Oneidea to support circuit switched services in LTE network is known as aterm CS fallback. CS fallback supports e.g. voice services andtraditional CS domain services (e.g. SMS) for LTE and the idea behindthe term is to reuse the GSM/WCDMA network resources for implementationof the mentioned services also in LTE. In practice this means that toimplement CS fallback functionality in LTE, all participating elementsi.e. UE, MME, MSC and E-UTRAN needs to support it.

FIG. 2 illustrates interfaces between different network elements indifferent networks. In order to enable the CS fallback functionalityinto the network a new interface SGs is added in LTE architecture. SGsalso includes short message service (SMS) functionality comprising SMSwithout CS fallback. The interface is the reference point between theMobility Management Entity (MME) in LTE and Mobile Switching Centreserver (MSC Server or MSS). SGs interface is used for the mobilitymanagement and paging procedures between packet switched and circuitswitched domains, and is based on the Gs interface procedures, which isknown from GSM/WCDMA.

In view of the current invention it is important to understand that forenabling CS fallback to operate the UE must register on both the LTE andGSM/WCDMA networks to insure that both networks are aware of itspresence and location. The UE does not have to perform two registrationprocedures, because LTE MME performs the registrations into bothnetworks, when the UE attaches to the LTE network. The registration onthe GSM/WCDMA network is performed in context of location update overthe SGs interface to the MSC in GSM/WCDMA network.

One benefit of CS fallback is that it extends the life of the GSM/WCDMAnetwork by enabling CS services, such as voice, for the LTE. Thus, e.g.telecom operators can get their investments worth, since the existingnetwork infrastructure can be utilized longer. Another benefit is thatCS fallback provides complete service and feature transparency with theGSM/WCDMA because the LTE subscriber is redirected to the GSM/WCDMAnetwork for all CS services.

The drawback of the CS fallback solution in general is that it causesheavy signaling between the networks. Additionally, the CS fallbackoperation may take a while to be established due to signaling and alsofor Quality of Service measurements if needed. This may be noticed bythe user.

One special case in CS fallback is that a user residing in LTE network(UE attached to LTE) wants to start CS based service, e.g. a voice call.In such a case UE sends a service request with the CS fallback indicatorto the MME. The request indicates that MME shall establish a CSfallback. MME requests the radio part (eNode B) of LTE redirect themobile device to the GSM/WCDMA network. In order to achieve theredirection on a radio layer the core network shall be controlled insuch a way that it can take the responsibility of the connectionmanagement. One important part of this is that there shall be a MSCserver dedicated for the UE for CS fallback situation. According to thecurrent practice a MSC server is randomly selected by the serving MMEfrom a pool of MSC servers according to a predefined algorithm (IMSIhash algorithm) when the UE enters to the LTE coverage. This happense.g. when the UE moves from GSM/WCDMA radio coverage to LTE radiocoverage. The problem with this approach is that by selecting a MSCserver randomly one needs to deliver subscriber information betweendifferent nodes as well as other information like location information.This, in turn, requires signaling between different network nodes aswell as may end up unbalanced load between different MSC servers. Thisis also unnecessary in a sense that when UE is moving from GSM/WCDMA toLTE, it already has a dedicated MSC server in GSM/WCDMA, which comprisesall necessary information relating to that specific UE.

The above described random selection of MSC happens also within SGSNbased MSC selection due to the fact that MSC Selection algorithm isconsistent between SGSNs and MMEs for so called combined registrationsover Gs and SGs interfaces. However, when a SGSN or a MME performs a MSCselection there is no consistency with a previous selection made for aUE that was registered via GERAN or RAN access. The inconsistency leadsto signaling traffic and thus to unnecessary load to the networks, asalready indicated.

More specifically, the root cause of the mismatch is that the selectionthat is performed via RAN and GERAN uses TMSI, as the NRI within theTMSI is the basis for the MSC Server Selection (in case of RAN, the UEmasks the relevant bits in the TMSI to construct the Intra Domain NASNode Selector (IDNNS), and in the case of GERAN the BSC uses the TMSIitself), but for combined attach the “IMSI hash” is the basis for MSCServer selection.

At least currently, LTE radio coverage is often limited which causes theCS fallback (CSFB) User Equipment to register to a Public Land MobileNetwork (PLMN) via GERAN. A typical case where location registrationwill be performed using Location Updating, an MSC Server will beselected, and the MSC Server will allocate a TMSI with an NRIidentifying the selected MSC Server. The NRI is subsequently re-used toidentify the MSC Server, and the same NRI is used at TMSI re-allocation,as long as the UE stays in the MSC Pool area. As long TMSI basedLocation Updating is used the same MSC Server is kept.

Considering that TMSI are allocated by different PLMNs and that in somecases the NRIs will match Core Network nodes between networks andsometimes will be subject to load balancing between the Core nodes, theUEs in the Core Network will be distributed over the MSC Servers in thepool not based on IMSI but on TMSI, even as historically there has tohave been an MSC selection performed using IMSI of the USIM.

In the case where the UE is CS fallback capable and detects LTE radiocoverage it will perform combined EPS/IMSI attach or combined trackingarea updating procedures, and the MME will select a MSC Server for theUE. The same will apply if the UE changes Radio Access Technology wherethe new RAT offers NMO=1 (Network Mode of Operation), and the old RAToffers a different NMO. In general, NMO is used to indicate if theregistration of the UE to the MSC and SGSM is combined (NMO=1) orindependent (NMO=2). In NMO=1 the SGSN selects the MSC Server with IMSIhash function.

Subsequent to the MME or SGSN selecting a new MSC Server for the UserEquipment, the MSC Server does not change again as long as the UEdoesn't change pool areas or re-selects PLMN, as the TMSI and NRI isallocated by the new MSC Server (barring load rebalancing).

Roaming CS fallback subscribers will cause MSC re-selection in theVisited Public Land Mobile Network (VPLMN) to be performed morefrequently as those UEs are subject to performing PLMN re-selection.Previously roaming subscribers returning to the Home Public Land MobileNetwork (HPLMN) will be allocated to the same MSC Server as previouslyif the NRI within the TMSI has not been changed by the remote network,but to a new MSC Server in other cases. For those UEs, an additionalchange of MSC Server will occur when the CS fallback User Equipmententers LTE coverage.

The change of MSC Server in the combined registration case issub-optimal, and in case of network disturbances or overload, it maydelay the recovery of the network. The case where the complete PS domainor EPS is unavailable for a period of time, may lead to furtherinstability in the CS domain when the PS domain or EPS recovers, due toextra signaling load for inter-MSC mobility.

However, the current 3GPP specification TS 23.236 V9.0.0 does not offera way to select MSC for CS fallback purposes. More precisely, there isno way to deliver information on the serving node between differentnetworks for such a purpose that the new network may need thatinformation in certain situations when offering service to the UE.

SUMMARY OF THE INVENTION

An objective of the invention is to present a method and an userequipment and a network node for minimizing signaling load on thenetwork. Another objective of the invention is that the method and theuser equipment and the network node enables balancing the subscriberload over a number of network nodes.

The objectives of the invention are achieved by introducing a novelmethod for managing the subscriber information in networks withdifferent communications technologies. More precisely, the objectives ofthe invention are achieved by minimizing the signaling on the network bydelivering information relating to serving network elements in acommunication network between the network elements belonging todifferent communication technologies.

Some aspects of the invention relate to a method for deliveringinformation on a serving mobile switching centre server for an userequipment between a first communication network and a secondcommunication network. The method comprises a step of requesting anattachment of the user equipment to the second communication network bysignaling between the user equipment and a network node of the secondcommunication network, the signaling comprising at least part ofinformation on the mobile switching centre server serving the userequipment in the first communication network.

Some aspects of the invention relate to an idea that the information onthe mobile switching centre server serving the user equipment in thefirst communication network is embedded in the TMSI information in thesignaling. For example, the NRI field of the TMSI information can beutilized.

Some aspects of the invention introduce that the NRI field comprisinginformation on the mobile switching centre server serving the userequipment in the first communication network is configured to beunspecified. Some additional aspects of the invention presents that theNRI field comprising information on the mobile switching centre serverserving the user equipment in the first communication network isconfigured to be arbitrary length, up to 10 bits.

Some aspects of the invention teach that the delivery of information isperformed over SGs interface.

Some additional aspects of the invention disclose that the informationon the mobile switching centre server serving the user equipment in thefirst communication network is stored in a network node of the secondcommunication network.

Further aspects of the invention say that the requesting of attachmentis delivered in response to quality of service measurement implementedby the user equipment.

Additionally, some aspects of the invention illustrate that the locationupdate procedure of the user equipment is performed at least to themobile switching centre server indicated in the attach request by thenetwork node.

Some aspects of the invention disclose that the full information of themobile switching center is composed from a multiple attach request, eachof the requests comprising at least part of the information on themobile switching centre server serving the user equipment in the firstcommunication network

Some aspects of a user equipment comprising a processor and at least amemory comprising software to be executed by the processor for creatinginstructions introduce that the user equipment is configured to insertat least part of information on a mobile communication centre serverserving the user equipment in a first communication network to a requestfor attaching the user equipment to a second communication network, therequest to be delivered to a network node residing in a secondcommunication network over a signaling layer. Further, the userequipment according to some aspects of the invention is configured todivide the information on the serving mobile communication centre serverinto multiple attach requests.

Some aspects of the invention relate to a network node comprising aprocessor and at least a memory comprising software to be executed bythe processor for creating instructions disclose that the network noderesiding in a second communication network is configured to derive atleast part of information on a mobile communication centre serverserving an user equipment in a first communication network from anattach request delivered by the user equipment to the network node overa signaling layer. Furthermore, the network node according to someaspects of the invention is configured to compose information on themobile communication centre server serving the user equipment in thefirst communication network from a multiple attach requests.

A method according to the invention is characterized by the stepsrecited in the characterizing part of the independent claim directed toa method.

An user equipment according to the invention is characterized by thefeatures recited in the characterizing part of the independent claimdirected to a device.

A network node according to the invention is characterized by thefeatures recited in the characterizing part of the independent claimdirected to a system.

The exemplary embodiments of the invention presented in this patentapplication are not to be interpreted to pose limitations to theapplicability of the appended claims. The verb “to comprise” is used inthis patent application as an open limitation that does not exclude theexistence of also unrecited features. The features recited in dependingclaims are mutually freely combinable unless otherwise explicitlystated.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an E-UTRAN attach procedure according to a 3GPPspecification,

FIG. 2 illustrates interfaces between different network elements indifferent networks,

FIG. 3 illustrates a flow chart relating to the method according to anembodiment of the invention,

FIG. 4 illustrates a structure of a data element according to anembodiment of the invention,

FIG. 5 illustrates an user equipment according to an embodiment of theinvention, and

FIG. 6 illustrates a network element according to an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION AND ITS ADVANTAGEOUS EMBODIMENTS

An exemplary embodiment of the invention is now described by firstreferring to FIG. 2 discussed shortly earlier. The user equipment UE 201comprises means for interacting with different communicationstechnologies, such as GSM and/or WCDMA and LTE. Thus, UE 201 is able tobe in connection to GERAN (GSM EDGE Radio Access Network) over Uminterface. Alternatively or in addition, the UE 201 is able to be inconnection to UTRAN (Universal Terrestrial Radio Access Network) overUu. Furthermore, the UE 201 comprise means for being interaction withthe radio access network elements of LTE technology i.e. eNode B 211over LTE-Uu interface. Both the GERAN and UTRAN are controlled by MSCserver over either interface A for GERAN 203 or interface lu for UTRAN205. Interface lu between UTRAN and MSC Servers is especially meant forCS service purposes. FIG. 2 illustrates two MSC servers A 207 and B 209.Moreover, the LTE radio access network elements eNode B 211 arecontrolled by Mobility Management Entity 213 over S1-MME interface. Itis to be noted that LTE network comprises multiple MMEs even if FIG. 2illustrates only one element. In order to manage connections and roamingaspects of UEs an interface SGs is configured to enable signalingbetween MME 213 and MSC 207; 209.

The invention is now discussed by referring to an attach proceduredescribed in FIG. 3. The situation as illustrated in FIG. 3 is that UE201 is moving from GSM/WCDMA network coverage to LTE coverage and it isdecided that the UE 201 shall be served by LTE network. This can resulte.g. from Quality of Service measurements implemented by the UE 201, forexample. The attach procedure illustrated in FIG. 3 is especially meantfor CS fallback situation i.e. how information necessary for CS fallbackis delivered from LTE network to GSM/WCDMA network in order to havenecessary support for CS connection in place if there is a need to offercircuit switched service to the UE 201.

More precisely, FIG. 3 illustrates the signaling between differententities of GSM/WCDMA and LTE networks. The network elements, inaddition to the network terminal UE, involved in the attach procedureare MME 123, MSC/VLR 207;209 and Home Subscriber Server (HSS) 303, whichis a master user database supporting network entities which handle thecalls. HSS 303 contains the subscription-related information (i.e.subscriber profiles), performs authentication and authorization of theuser, and can provide information about the subscriber's location and IPinformation. HSS 303 performs similar tasks to the GSM Home LocationRegister (HLR) and Authentication Centre (AuC). It is illustrated onlythose elements here, which relate to attach procedure especially forenabling CS fallback in such a way that signaling can be minimized.

The attach procedure initiates with an attach request 311 delivered byan UE 201 to eNode B 211 and further to the MME 213 serving the eNode B211. The attach request message comprises multiple type of information,i.e.

-   -   International Mobile Subscriber Identity (IMSI) or old Globally        Unique    -   Temporary Identity (GUTI)    -   Old GUTI type    -   last visited Tracking Area Identity (TAI) (if available)    -   UE Core Network Capability    -   UE Specific Discontinuous Reception (DRX) parameters    -   Attach Type    -   Evolved Session Management (ESM) message container (Request        Type, PDN Type, Protocol Configuration Options, Ciphered Options        Transfer Flag)    -   Key identifier KSI_(ASME) for authenticating UE SIM/USIM    -   Non-access stratum (NAS) sequence number    -   NAS-MAC    -   additional GUTI    -   P-Temporary Mobile Subscriber Identity (TMSI) signature for        packet domain service in GSM and WCDMA    -   Voice domain preference for prioritizing voice or data service    -   UE's usage setting    -   MS Network Capability

In addition to the attach request message also RRC parameters indicatingthe Selected Network and the old GUMMEI Globally Unique MME Identifier.For CS fallback purposes the Attach Type information in the attachrequest message indicates that the UE requests a combined EPS/IMSIattach and informs the network that the UE is capable and configured touse CS fallback and/or SMS over SGs interface.

According to the invention a new information element is added to theabove described attach request. More specifically, information on theMSC server 207;209, which is serving the UE 201 in GSM/WCDMA network, isdelivered along the attach request 311 to a network node in LTE network.According to an embodiment of the invention an information element MSIdentity is added to the signaling carried out over SGs interface. TheMS Identity is configured to be a new identifier comprising TemporaryMobile Subscriber Identity (TMSI) comprise information on the MSC server207;209, which is serving the UE in the GSM/WCDMA network. Moreprecisely, information on the MSC server 207;209 is embedded to aNetwork Resource Identifier (NRI) field of the TMSI informationaccording to the embodiment of the invention. MS Identity comprisingTMSI is a new information element added to attach request. It shall notbe mixed with P-TMSI described above due to the fact that TMSI accordingto the invention comprises a NRI field indicating MSC server, but P-TMSIcomprises a NRI field pointing out SGSN (Serving GPRS serving node) in aSGSN pool. Thus, P-TMSI is outside of the scope of the currentinvention.

Generally speaking, TMSI is the identity that is sent between the UE andthe network assigned by MSC/VLR to every UE within the area. Key use ofthe TMSI is in paging the mobile within the network. Thus, one of theinventive aspects of the current invention is that the TMSI comprises aninformation field called NRI, which is not specified, but it is stillpart of the TMSI. Thus, by including TMSI in the attach request it doesnot require any further modification to the system. The only need forthe NRI is to be parsed from the TMSI in the same way as the NRI isparsed from the TMSI in the GERAN radio network in order to being ableto derive information on the MSC server embedded in the NRI field. TheUser Equipment is not aware, which part of the TMSI is used for the NRI,so the UE cannot identify the NRI.

The MME receiving the attach request is configured to analyze thereceived request signaling and deriving delivered MSC server informationfrom the request. In response to derivation of MSC server informationfrom the attach request the network node, e.g. MME, may store theinformation to its memory according to an embodiment of the invention.

The next phase 312 of the attach procedure for confirming the CSfallback comprises the similar steps from 3 to 16 as described inFIG. 1. Since they do not have any impact to the invention they need notto be discussed here.

In phase 313 the MME 213 is configured to derive Visitor LocationRegister (VLR) number based on the NRI value the MME 213 has stored forthe MSC/VLR. The VLR is a database of the subscribers who have roamedinto the area of the MSC (Mobile Switching Center) which it serves. Inresponse to the derived VLR number the MME 213 starts location updateprocedure towards the MSC/VLR 207;209, which serves the UE 201currently, by sending a location update request 314 to the MSC/VLR207;209. An interface SGs is associated 315 between the MME 213 and theMSC/VLR 207;209, which is currently serving the UE 201 in GSM/WCDMA.Furthermore, as normal the location update 316 in CS domain isconfigured to be established by MSC 207;209 and the HSS 303. Thelocation update is confirmed to MME 213 with an acceptance signaling317. Finally, the attach procedure is finalized 318 according to stepsfrom 17 to 26 as illustrated in FIG. 1, which are not discussed here.

As disclosed, information on the MSC server 207;209, which is servingthe UE 201, is delivered in the attach request. More precisely, theinformation is delivered in TMSI. FIG. 4 illustrates the structure ofTMSI 401. TMSI 401 is an identifier with a length of 32 bits. The NRI isa part of the TMSI 401. It is not fixed length, but the maximum lengthis 10 bits. The utilization of NRI field in TMSI 401 is based on thefact that one or more specific NRI is assigned to every MSC. One ofthese specific NRIs is part of every temporary identity TMSI 401 whichthe MSC assigns to an UE. The location of bits indicating the MSCidentity may be agreed beforehand, but it is advantageous to leave thestructure unspecified to allow the flexibility in the system. Forexample, according to an embodiment of the invention the MSC server maybe identified as an index of 4 bits, identifying null which is spare,and MSC Servers 1 through 15. This index is called the NRI. The NRI can,however, be of an arbitrary length, up to 10 bits. The length depends atleast on the implementation of the network i.e. how many MSC Servers areneeded to cover the management of the radio access network and/or UEs.In addition to NRI field the TMSI may comprise other information fieldssuch as VLR restart field. The TMSI structure is modifiable.

As can be concluded from the description above the method according toan embodiment of the invention minimizes the signaling required forenabling the CS fallback. This is achieved by transferring informationrelating to MSC server, which is serving the UE in GSM/WCDMA networkconnections, to MME of LTE network in attach request for LTE network. Asa result, the MME does not have to assign a randomly selected MSC serverfor the UE attached to it. As a result, there is no need for additionalsignaling when assigning MSC server or in the context of locationupdate.

According to some other embodiment of the invention only part of theinformation on the mobile switching centre server serving the userequipment in the first communication network is delivered in the attachrequest from UE to MME via the radio access network. Thus, an attachrequest comprises at least part of the information on the MSC server,which is serving the UE in GSM/WCDMA network. As a result information onthe MSC server, which is serving the UE in GSM/WCDMA network, can betransmitted in one or more attach requests. The MME is configured tocompose the full information of the MSC server, which is serving the UEin GSM/WCDMA network, from multiple attach requests.

In the description of the invention it has been referred to deliveringinformation on the MSC server, which is serving UE in GSM/WCDMA network,to the MME. The same inventive idea is applicable in deliveringinformation on the MSC server, which is serving UE in GSM/WCDMA network,to the SGSN using the Gs interface in place of the SGs interface, andusing the NRI within the TMSI accordingly. Gs is the interface betweenthe SGSN and MSC server elements. The delivery of the information on theMSC server, which is serving the UE, to the SGSN, is important accordingto the invention due to the fact that by means of this one can preventthe re-selection of MSC server by SGSN in case of NMO=1. SGSN is notillustrated in FIG. 2 for clarity reasons.

The invention also relates to the user equipment UE. According to anembodiment of the invention the UE comprises a processing component thatis capable of executing instructions related to the actions describedabove. FIG. 5 illustrates an example of a UE that comprises a processingcomponent 501 suitable for implementing one or more embodimentsdisclosed herein. In addition to the processor 501 (or Central ProcessorUnit; CPU), the UE may comprises network connectivity elements 502,random access memory (RAM) 503, read only memory (ROM) 504 andinput/output (I/O) devices 505. Additionally, the UE may comprise asmart card 506, such as SIM and/or USIM, for storing network-specificinformation used to authenticate and identify subscribers on thenetwork. These components may communicate with one another via a bus507. In some cases, at least some of these components can locate in asingle physical entity or in more than one physical entity.

The processor 501 is configured to execute instructions, codes computerprograms or scripts, which can be accessed via network connectivityelements 502, or from RAM 503, ROM 504 or smart card coupled to UE 506.While only one processor is disclosed in FIG. 5, multiple processors maybe present.

The network connectivity elements may comprise e.g. modems, Ethernetdevices, universal serial bus (USB) interface devices, wireless localarea (WLAN) devices, radio transceiver devices, such as GSM radiotransceiver devices, WCDMA radio transceiver devices and/or LTE radiotransceiver devices. The network connectivity elements may enable theprocessor to communicate with the corresponding telecommunicationnetworks or Internet or other networks.

The RAM can be used to store volatile data and instructions that areexecuted by the processor. The ROM is a non-volatile memory and it isused to store instructions and perhaps data that are read duringexecution of instructions.

The I/O devices may include displays, touch screen displays, keyboards,keypads, switches, mice, track balls, voice recognizers, card readers,or other known I/O devices.

According to an embodiment of the invention the UE comprises softwarestored in the memory elements and executed by the processor to detectthe need for attaching to a new network. The detection can be a resultof execution of channel measurements in order to maintain connectivityto the most appropriate network in an area. If a need changing from afirst telecommunication network, such as GSM or WCDMA, to a secondnetwork, such as LTE, is detected, the UE is configured to compose aattach request signaling for LTE network. The composing of the requestcomprises a step of inserting at least part of the information on theMSC server, which serves it in GSM and/or WCDMA network, into therequest. Thus, the processor is instructed to derive information on theserving MSC in GSM and/or WCDMA from TMSI information, which is theidentity that is sent between the UE and the network, and insert thatinto the attach request. More specifically, the memory elements of UEcomprise instructions to insert at least part of the information on theMSC server serving UE in GSM and/or WCDMA into the TMSI informationelement, and especially into the NRI field. Furthermore, the UE isconfigured to deliver the attach request to the MME in LTE network viaeNode B. The LTE-Uu interface between UE and eNode B and S1-MMEinterface between the eNode B and MME are utilized in the signaling. Theconnectivity elements of the UE are configured to implement acorresponding interface, such as LTE-Uu, towards the network nodes, suchas eNode B. If the UE composes an attach request comprising only part ofthe information on the serving MSC server, the UE is configured todetect this and compose multiple attach requests, each comprising atleast part of the information. The full information is configured to bedelivered over the signaling.

According to an embodiment of the invention the above describedimplementation of MSC server information delivery by the UE is performedby means of the processor and software comprising instructions forimplementing it when the software is executed by the processor of theUE.

Correspondingly, according to an embodiment of the invention a networknode being a counterpart in the communication to the UE, such as theMME, comprises a processing component that is capable of executinginstructions related to the actions described above. FIG. 6 illustratesan example of a MME that comprises a processing component 601 suitablefor implementing one or more embodiments disclosed herein. In additionto the processor 601 (or Central Processor Unit; CPU), the MME maycomprises network connectivity elements 602, random access memory (RAM)603, read only memory (ROM) 604 and input/output (I/O) devices 605.These components may communicate with one another via a bus 607. In somecases, at least some of these components can locate in a single physicalentity or in more than one physical entity.

The processor 601 is configured to execute instructions, codes computerprograms or scripts, which can be accessed via network connectivityelements 602, or from RAM 603 or ROM 604. While only one processor isdisclosed in FIG. 6, multiple processors may be present.

The network connectivity elements may comprise e.g. modems, Ethernetdevices, universal serial bus (USB) interface devices, wireless localarea (WLAN) devices, radio transceiver devices, such as GSM radiotransceiver devices, WCDMA radio transceiver devices and/or LTE radiotransceiver devices. The network connectivity elements may enable theprocessor to communicate with the corresponding telecommunicationnetworks or Internet or other networks over the known interfaces. Forexample, the network connectivity elements of MME are configured toimplement S1-MME interface towards eNode B and SGs interface towards oneor more MSC servers.

The RAM can be used to store volatile data and instructions that areexecuted by the processor. The ROM is a non-volatile memory and it isused to store instructions and perhaps data that are read duringexecution of instructions.

The I/O devices may include displays, touch screen displays, keyboards,keypads, switches, mice, track balls, voice recognizers, card readers,or other known I/O devices.

According to an embodiment of the invention the MME comprises softwarestored in the memory elements and executed by the processor to detect aattach request over signaling layer from a UE delivered via eNode B orSGSN. The processor when executing the software is configured to analyzethe received attach request and derive TMSI information from therequest. Furthermore, the MME is configured to derive NRI informationinside the TMSI and especially to derive at least part of information ona MSC server, which is serving the UE in a network from which the UE isattaching to LTE network. In response of detecting and deriving theinformation on the MSC server, the MME is configured to store theappropriate information from the attach request into its memoryaccording to an embodiment of the invention. Thus, the MME is configuredto perform location update procedure towards the MSC/VLR. Especially, ina CS fallback situation the MME is configured to check the MSCinformation from its memory and implement the CS connection by means ofthe MSC. If the network node detects that only part of the informationon a mobile communication centre server serving an user equipment in afirst communication network is delivered in a single attach request, thenetwork node is configured to compose the full information on the mobilecommunication centre server serving the user equipment in the firstcommunication network from a multiple attach requests.

According to an embodiment of the invention the above describedimplementation of MSC server information delivery to MME is performed bymeans of the processor and software comprising instructions forimplementing it when the software is executed by the processor of MME orany other processing means serving the MME.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented. For example, theterminology GSM/WCDMA in the description is to be understood in such amanner that it indicates only GSM network or only WCDMA network or bothof the networks.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

1. A method for delivering information on a serving mobile switchingcentre server for an user equipment between a first communicationnetwork and a second communication network, the method comprising a stepof requesting an attachment of the user equipment to the secondcommunication network by signaling between the user equipment and anetwork node of the second communication network, the signalingcomprising at least part of information on the mobile switching centreserver serving the user equipment in the first communication network. 2.A method as claimed in claim 1, wherein the information on the mobileswitching centre server serving the user equipment in the firstcommunication network is embedded in the TMSI information in thesignaling.
 3. A method as claimed in claim 2, wherein the information onthe mobile switching centre server serving the user equipment in thefirst communication network is embedded in the NRI field of the TMSIinformation.
 4. A method as claimed in claim 3, wherein the structure ofthe NRI field comprising information on the mobile switching centreserver serving the user equipment in the first communication network isconfigured to be unspecified.
 5. A method as claimed in claim 3, whereinthe NRI field comprising information on the mobile switching centreserver serving the user equipment in the first communication network isconfigured to be arbitrary length, up to 10 bits.
 6. A method as claimedin claim 1, wherein the delivery of information is performed over SGsinterface.
 7. A method as claimed in claim 1, wherein the information onthe mobile switching centre server serving the user equipment in thefirst communication network is stored in a network node of the secondcommunication network.
 8. A method as claimed in claim 1, wherein therequesting of attachment is delivered in response to quality of servicemeasurement implemented by the user equipment.
 9. A method as claimed inclaim 1, wherein a location update procedure of the user equipment isperformed at least to the mobile switching centre server indicated inthe attach request by the network node.
 10. A method as claimed in claim1, wherein full information of the mobile switching center is composedfrom a multiple attach request, each of the requests comprising at leastpart of the information on the mobile switching centre server servingthe user equipment in the first communication network.
 11. A userequipment comprising a processor, at least a memory comprising softwareto be executed by the processor for creating instructions, wherein theuser equipment is configured to insert at least part of information on amobile communication centre server serving the user equipment in a firstcommunication network to a request for attaching the user equipment to asecond communication network, the request to be delivered to a networknode residing in a second communication network over a signaling layer.12. A user equipment as claimed in claim 11, wherein the user equipmentis configured to divide the information on the serving mobilecommunication centre server into multiple attach requests.
 13. A networknode comprising a processor, at least a memory comprising software to beexecuted by the processor for creating instructions, wherein the networknode residing in a second communication network is configured to deriveat least part of information on a mobile communication centre serverserving an user equipment in a first communication network from anattach request delivered by the user equipment to the network node overa signaling layer.
 14. A network node as claimed in claim 13, whereinthe network node is configured to compose information on the mobilecommunication centre server serving the user equipment in the firstcommunication network from a multiple attach requests.
 15. A method asclaimed in claim 4, wherein the NRI field comprising information on themobile switching centre server serving the user equipment in the firstcommunication network is configured to be arbitrary length, up to 10bits.